JP6733615B2 - Heat storage device - Google Patents

Description

The present invention relates to a heat storage device.

Patent Document 1 discloses a heat storage system using sodium acetate trihydrate as a heat storage material.

Sodium acetate trihydrate melts at a melting point of 58°C. However, sodium acetate trihydrate does not solidify immediately when cooled below its melting point. A state in which the liquid is not solidified even when cooled to the melting point or lower is called a supercooled state.

After the heat storage material containing sodium acetate trihydrate is heated and melted, the heat storage material is cooled to a supercooled state. In this way, latent heat is stored in sodium acetate trihydrate. When heat is needed, the supercooled state of the heat storage material containing sodium acetate trihydrate is released. Sodium acetate trihydrate changes from a liquid state to a solid state, and this change releases heat from sodium acetate trihydrate. That is, latent heat is extracted. In this way, the heat storage effect is achieved.

Patent Document 2 discloses a heat storage tank including a silver electrode for applying a voltage to a heat storage material in a supercooled state, as a means for releasing the supercooled state.

Patent Document 3 discloses a supercooling inhibitor, a heat storage method, and a heat storage system. The manufacturing method according to Patent Document 3 includes a step of immersing the porous body in a melt containing sodium acetate trihydrate, and a temperature at which the supercooling of the melt is released while maintaining the state in which the porous body is impregnated with the melt. The step of cooling the melt and the porous body is included below. Heat is stored by heating a heat storage material containing sodium acetate trihydrate at a temperature higher than the melting point of sodium acetate trihydrate. In the presence of the supercooling inhibitor produced by the method according to Patent Document 3, heat is removed from the heat storage material so that sodium acetate trihydrate changes from a liquid phase to a solid phase.

JP, 2008-20177, A JP-A-61-204293 JP, 2013-067720, A

An object of the present invention is to provide a heat storage device which releases supercooling by applying a voltage to release heat and which can be repeatedly used.

The present invention is a heat storage device,
Heat storage material containing sodium acetate trihydrate,
A first electrode which is in contact with the heat storage material and has a surface formed of at least one selected from the group consisting of silver, silver alloys, and silver compounds;
A second electrode in contact with the heat storage material,
An inorganic porous material contained in the heat storage material, and a power source for applying a voltage to the first electrode and the second electrode,
The inorganic porous body is a heat storage device having an average pore diameter of 50 nanometers or less.

The present invention includes a heat release method using the above heat storage device.

The present invention includes a vehicle including the above heat storage device. Further, the invention includes a method of applying heat to an engine in the vehicle.

The present invention provides a heat storage device that releases supercooling by applying a voltage to release heat and can be repeatedly used.

FIG. 1 shows a schematic view of a heat storage device according to an embodiment. FIG. 2 shows a schematic diagram of the pore structure of activated carbon.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Heat storage device 10)
FIG. 1 shows a schematic diagram of a heat storage device 10 according to an embodiment. In FIG. 1, the heat storage device 10 includes a heat storage tank 11 filled with a heat storage material 12, a pair of electrodes 13 having a first electrode 13 a and a second electrode 13 b, a DC power supply 14, and a switch 15.

(Heat storage tank 11)
The heat storage tank 11 is kept warm by a heat insulating material. An example of an insulating material is glass wool. The heat storage tank 11 contains a heat storage material 12. In the present embodiment, the heat storage material 12 is sodium acetate trihydrate. In other words, the heat storage material 12 contains sodium acetate trihydrate as a main component.

(Heat storage material 12)
The heat storage material 12 contains an inorganic porous body.

As will be described in detail later, the present inventors believe that the inside of the pores of the inorganic porous material has a fine solid phase heat storage material 12. In the present specification, the solid phase fine heat storage material 12 is also referred to as a “cluster”. The solid phase fine heat storage material 12 contained in the pores has a stronger intermolecular bond than the heat storage material 12 located outside the pores due to capillary condensation.

Therefore, when the heat storage material 12 is heated, the heat storage material 12 contained in the pores melts more slowly than the heat storage material 12 located outside the pores. As a result, it is possible to increase the viability of the clusters after the heat storage material 12 is held at a high temperature in the liquid state. Therefore, even after the heat storage material 12 is kept at a high temperature in the liquid state, the supercooled state of sodium acetate trihydrate can be released under the temperature of 58 degrees Celsius or less by applying the voltage. More specifically, even after the heat storage material 12 is kept in a liquid state at a high temperature, the clusters (that is, the solid phase fine heat storage material 12) are located in the pores, so that the supercooled state is obtained. When the voltage at is applied, the heat storage material 12 is crystallized so as to spread from the center of the cluster to the periphery thereof. In other words, the crystallization of the heat storage material 12 at the time of applying the voltage in the supercooled state starts from the cluster.

The inorganic porous material contained in the heat storage material 12 has an average pore diameter of 50 nanometers or less.
The pore size of the inorganic porous material can be measured by a commonly used method. For example, the pore size can be calculated based on the nitrogen gas adsorption method or the mercury porosimetry method. As used herein, the term “average pore size” means the adsorption isotherm of nitrogen by the Barret-Joyner-Halenda method (hereinafter referred to as “BJH method”) or Horvath-Kawazoe method (hereinafter referred to as “HK method”). Means the pore diameter at the peak value of the pore diameter distribution curve derived from. The pore diameter distribution curve is drawn on a graph in which the horizontal axis represents the pore diameter and the vertical axis represents the pore volume. The average pore diameter is equal to the pore diameter at the maximum pore volume. Alternatively, the term “average pore size” used in the present specification means the pore size at the peak value of the pore size distribution curve obtained by the mercury penetration method. In the present specification, the average pore size of zeolite, mesoporous silica, or activated carbon is calculated by the nitrogen gas adsorption method. The average pore diameter of silica gel is calculated by the mercury intrusion method. In many cases, the average pore size of commercially available inorganic porous materials is disclosed in the catalog.

As demonstrated in Comparative Example 2 to be described later, when the average pore diameter exceeds 50 nanometers, sodium acetate trihydrate even if a voltage is applied after the heat storage material 12 is kept at a high temperature in a liquid state. The supercooled state of Japanese products is not released. This is because when the average pore diameter exceeds 50 nanometers, the effect of capillary condensation is reduced, so that the viability of clusters after the heat storage material 12 is kept at a high temperature in a liquid state is significantly reduced. The inventors consider that. Needless to say, even when the heat storage material 12 does not contain an inorganic porous material, the supercooled state of sodium acetate trihydrate is not released for the same reason as above.

On the other hand, the lower limit of the average pore diameter of the inorganic porous material is not limited as long as the pores have the heat storage material 12 and the melting of the clusters is suppressed. As an example, the average pore diameter of the inorganic porous material is 0.9 nanometers or more.

The material of the inorganic porous body is, for example, metal oxide or carbon. Examples of metal oxides are zeolite, silica, alumina, titania, or tungsten oxide.

As demonstrated in the examples below, the preferred inorganic porous material is activated carbon or silica gel.

Activated carbon and silica gel have pores having a size of 50 nanometers or less (hereinafter referred to as “micro mesopores”), and pores connected to these pores and having a size of more than 50 nanometers (hereinafter , "Macropores") on its surface.

FIG. 2 shows a schematic diagram of the structure of the pores of the inorganic porous material. As shown in FIG. 2, the surface 20 of activated carbon has macropores 21. The micro mesopores 22 are arranged inside the activated carbon so as to be connected to the macropores 21. Therefore, the heat storage material 12 is easily introduced into the micro mesopores 22. In this way, the solid phase fine heat storage material 12 is formed inside the micro mesopores. This will be described later in detail.

As a result, more heat storage material 12 can be arranged in the micro mesopores 22 having a size of 50 nanometers or less, as compared with the inorganic porous body having no macropores 21 such as mesoporous silica. As a result, the cluster survival rate after the heat storage material 12 is kept at a high temperature in the liquid state is further improved. Therefore, even if the heat storage material 12 is kept in a liquid state at a high temperature for a long time, the supercooling can be released by applying the voltage.

The heat storage material 12 may include an additive. Examples of additives include supercooling release aids, viscosity modifiers, foam stabilizers, antioxidants, defoamers, abrasive grains, fillers, pigments, dyes, colorants, thickeners, surfactants, difficult agents. It is a flame retardant, a plasticizer, a lubricant, an antistatic agent, a heat stabilizer, a tackifier, a curing catalyst, a stabilizer, a silane coupling agent, or a wax. The kind and amount of the additive are not limited as long as the object of the present invention is not impaired. Additives need not be added to the heat storage material 12.

(Method of forming solid phase fine heat storage material 12 in pores of inorganic porous body)
A method for forming the solid phase fine heat storage material 12 in the pores of the inorganic porous body will be described below. The heat storage material 12 containing the inorganic porous material is heated at a temperature equal to or higher than the melting point (that is, 58 degrees Celsius) of the heat storage material 12. In this way, the heat storage material 12 becomes liquid. Next, while maintaining this temperature, the heat storage material 12 is left standing for a predetermined time. During this time, the heat storage material 12 is introduced into the pores of the inorganic porous body. The present inventors believe that the heat storage material 12 is introduced into the pores of the inorganic porous body due to the capillary phenomenon.

Then, the heat storage material 12 is cooled at a temperature of -30 degrees Celsius or lower. Alternatively, the heat storage material 12 is cooled to 58 degrees Celsius or less, becomes a supercooled state, and then a seed crystal made of sodium acetate trihydrate is added to the heat storage material 12. The heat storage material 12 in the pores is crystallized by adding the seed crystal in a cooled state or a supercooled state at a low temperature of -30 degrees Celsius or less. That is, the heat storage material 12 in the pores changes from the liquid phase to the solid phase. In this way, the solid phase fine heat storage material 12 can be formed in the pores of the inorganic porous body.

(Electrodes, power supplies, and switches)
As shown in FIG. 1, the first electrode 13 a and the second electrode 13 b are electrically connected to the power supply 14 via the wiring and the switch 15 .

Both the first electrode 13a and the second electrode 13b are arranged so as to contact the heat storage material 12. The distance between the first electrode 13a and the second electrode 13b in the portion in contact with the heat storage material 12 is not particularly limited. An example of the distance is 1 mm or more and 30 mm or less.

The first electrode 13a has silver, a silver alloy, or a silver compound on its surface. Needless to say, the silver or its alloy is in contact with the heat storage material 12. Examples of silver alloys are silver-palladium alloys or silver-copper alloys. Examples of silver compounds are silver halide or silver oxide. An example of silver halide is silver bromide.

The second electrode 13b does not need to have silver, a silver alloy, or a silver compound on its surface. Needless to say, the second electrode 13b may also have silver, a silver alloy, or a silver compound on its surface.

The shapes of the first electrode 13a and the second electrode 13b are not limited. The shape of the first electrode 13a and the second electrode 13b is, for example, a plate shape or a linear shape.

Instead of the DC power supply 14, an AC power supply may be used.

The heat storage device 10 according to the present embodiment may include a plurality of heat storage tanks 11. Each heat storage tank 11 may include a first electrode 13 a and a second electrode 13 b that are in contact with each heat storage material 12. The plurality of heat storage tanks 11 can be electrically connected in parallel to the DC power supply 14.

(How to use the heat storage device 10)
First, the heat storage material 12 is cooled and brought into a supercooled state. In this way, latent heat is stored in sodium acetate trihydrate.

Next, a voltage is applied between the first electrode 13a and the second electrode 13b, and the supercooled state of the heat storage material 12 is released. By releasing the supercooled state of the heat storage material 12 by applying a voltage, the heat storage material 1
2 crystallizes. As a result, the heat storage material 12 releases heat. That is, latent heat is extracted.

(Reuse of heat storage device 10)
After the heat storage material 12 releases heat, the heat storage device is heated at a temperature of not lower than 58 degrees Celsius and not higher than 80 degrees Celsius for repeated use. In this way, the sodium acetate trihydrate contained in the heat storage material 12 melts. In other words, the crystallized sodium acetate trihydrate (ie solid state sodium acetate trihydrate) melts upon heating. The heat storage material 12 should not be heated at a temperature higher than 90 degrees Celsius. In the unlikely event that the heat storage material 12 is heated at a temperature of 90 degrees Celsius or higher, the viability of the cluster is significantly reduced as shown in Comparative Examples 4 to 12.

However, even when the heat storage material 12 is heated at a temperature of 90 degrees Celsius or higher, the pores of the inorganic porous material can be obtained by adding a seed crystal in a cooling or supercooling state at a low temperature of -30 degrees Celsius or lower. The solid phase fine heat storage material 12 can be formed therein again.

(Example)
The invention will be described in more detail with reference to the following examples.

(Example 1)
Example 1 is composed of Examples 1A to 1D.

(Example 1A)
(Production of heat storage device 10)
To the heat storage tank 11 was added sodium acetate (2.2 grams), water (1.8 grams), and zeolite with an average pore size of 0.9 nanometers. The heat storage tank 11 was a glass sample bottle having a capacity of 9 ml. Zeolite was purchased from Tosoh Corporation under the trade name “X-type zeolite, F-9”. The amount of zeolite added was 20% by mass based on the total weight of sodium acetate and water (ie 4.0 g). In other words, the amount of zeolite added was 0.8 grams. In this way, the heat storage material 12 containing zeolite and containing sodium acetate trihydrate as a main component was stored in the heat storage tank 11.

Next, the first electrode 13a and the second electrode 13b made of linear silver were immersed in the heat storage material 12. The first electrode 13a and the second electrode 13b had a diameter of 1.5 millimeters. The length of the portion where the first electrode 13a and the second electrode 13b were in contact with the heat storage material 12 was approximately 5 millimeters. The heat storage tank 11 was covered with a lid. In this way, the heat storage device 10 according to Example 1 was obtained.

(Evaluation of the heat storage device 10)
The liquid heat storage material 12 contained in the heat storage tank 11 was allowed to stand at a temperature of 70 degrees Celsius for 2 hours. The present inventors consider that the heat storage material 12 has entered the pores of the zeolite during this period. Then, the heat storage material 12 was cooled to -30 degrees Celsius. In this way, the heat storage material 12 was crystallized. The present inventors considered that both the heat storage material 12 inside the pores and the heat storage material 12 outside the pores changed from the liquid state to the solid state.

Next, the heat storage material 12 contained in the heat storage tank 11 was heated at a temperature of 70 degrees Celsius for 1 hour. As a result, the heat storage material 12 melted. Next, the heat storage material 12 was allowed to stand at a standing temperature of 80 degrees Celsius for a standing time of 15 minutes. Furthermore, the heat storage material 12 was cooled to room temperature (about 25 degrees Celsius). A voltage of 2 volts was applied between the first electrode 13a and the second electrode 13b for about 2 minutes, and the present inventors visually observed whether the heat storage material 12 was crystallized. The evaluation was repeated 6 times. Table 1 shows the observation results. The fractional numerator included in Table 1 is the number of times the heat storage material 12 was crystallized. The denominator of the fraction included in Table 1 is the number of evaluations (that is, 6 times).

(Examples 1B to 1D)
In Examples 1B to 1D, the same experiment as in Example 1A was performed, except that the standing time was 30 minutes, 1 hour, and 2 hours, respectively. The experimental results are shown in Table 1.

(Example 2)
The same experiment as in Example 1 was performed except for the following matters (i) and (ii).

(I) Mesoporous silica (purchased from Sigma-Aldrich under the trade name "MCM-41", average pore diameter: 2.5 nanometers to 3.0 nanometers) was used in place of zeolite, and (ii) ) The amount of mesoporous silica added was 15% by mass (ie, 0.6 g) based on the total weight of sodium acetate and water (ie, 4.0 g).

(Example 3)
The same experiment as in Example 1 was performed except for the following matter (i).

(I) Instead of zeolite, activated carbon (purchased from Calgon Carbon Japan Co., Ltd. under the trade name of "coconut shell activated carbon", average pore diameter: 1.0 nanometer to 3.0 nanometer) was used.

(Example 4)
The same experiment as in Example 1 was performed except for the following matter (i).

(I) Instead of zeolite, silica gel (purchased from Fuji Silysia Chemical Ltd. under the trade name “MB100”, average pore diameter: 10 nanometers) was used.

(Example 5)
The same experiment as in Example 1 was performed except for the following matter (i).

(I) Instead of zeolite, silica gel (purchased from Fuji Silysia Chemical Ltd. under the trade name “MB300”, average pore diameter: 30 nanometers) was used.

(Example 6)
The same experiment as in Example 1 was performed except for the following matter (i).

(I) Instead of zeolite, silica gel (purchased from Fuji Silysia Chemical Ltd. under the trade name “MB500”, average pore diameter: 50 nanometers) was used.

(Comparative Example 1)
The same experiment as in Example 1 was performed, except that zeolite was not added to the heat storage tank 11.

(Comparative example 2)
The same experiment as in Example 1 was performed except for the following matter (i).

(I) Instead of zeolite, silica gel (purchased from Fuji Silysia Chemical Ltd. under the trade name “MB800”, average pore diameter: 80 nanometers) was used.

(Comparative example 3)
The same experiment as in Example 1 was performed except for the following matter (i).

(I) Silica (purchased from Kanto Chemical Co., Inc.) was used instead of zeolite. The silica was formed from non-porous amorphous silicon dioxide.

(Comparative Examples 4 to 12)
The same experiment as in Examples 1 to 6 and Comparative Examples 1 to 3 was performed, except that the standing temperature was 90 degrees Celsius. The results are shown in Table 2.

As is clear from Table 1 and Table 2, the stationary temperature needs to be 80 degrees Celsius or less. Otherwise, crystallization of the heat storage material 12 often fails. As is clear from Table 1, the average pore size needs to be 50 nanometers or less. Otherwise, crystallization of the heat storage material 12 often fails.

As is clear from Table 1, the inorganic porous material is preferably silica gel or activated carbon from the viewpoint of the reliability of crystallization of the heat storage material 12.

As shown in the above example, by adding an inorganic porous material having an average pore diameter of 50 nanometers or less to the heat storage material 12, the heat storage material 12 has a melting point (that is, 58 degrees Celsius or more) and 80 degrees Celsius. The latent heat can be taken out by applying a voltage even after the latent heat is maintained at a high temperature of not more than 10 degrees.

In the heat storage device according to the present invention, latent heat can be taken out by applying a voltage even after the heat storage material 12 is held in a liquid state at a high temperature.

As an example, the heat storage device according to the present invention is attached to a vehicle including an engine that drives wheels. The heat released from the heat storage material 12 is used for warm-up operation of an internal combustion engine such as an engine provided in the vehicle. The heat storage device according to the present invention is also attached to a boiler, an air conditioner or a water heater.

10 Thermal Storage Device 11 Thermal Storage Tank 12 Thermal Storage Material 13 Electrode 14 DC Power Supply 15 Switch 20 Activated Carbon Surface 21 Macropore 22 Micro Mesopore

Claims (6)

A method of releasing heat, comprising the steps of:
(Pa1) a step of crystallizing a heat storage material containing sodium acetate trihydrate,
(Pa2) a step of melting the heat storage material at 80 degrees Celsius or less after the step (pa1),
(A) cooling a heat storage device including the heat storage material to bring the sodium acetate trihydrate into a supercooled state,
here,
The heat storage device,
The heat storage material in contact, and silver, a silver alloy or a first electrode having a surface formed from a silver compound,,
A second electrode in contact with the heat storage material,
An inorganic porous material contained in the heat storage material; and a power supply for applying a voltage to the first electrode and the second electrode,
The inorganic porous material has an average pore diameter of 10 nanometers or more and 50 nanometers or less, and the inorganic porous material is formed of silica gel,
(B) a step of applying a voltage to the first electrode and the second electrode at a temperature of 58 degrees Celsius or lower after the step (a) to release heat from the heat storage material; and (C) A method comprising the step of, after the step (b), heating the heat storage device at a temperature of 58° C. or higher and 80° C. or lower to melt the sodium acetate trihydrate. The method of claim 1, wherein
The step (pa1) is
(Pa11) A method comprising a step of cooling the heat storage material to -30 degrees Celsius or less. The method of claim 1, wherein
The step (pa1) is
(Pa12) A method comprising a step of adding crystals of sodium acetate trihydrate to the supercooled heat storage material. A method of applying heat to an engine included in a vehicle, comprising the steps of:
(Pa1) a step of crystallizing a heat storage material containing sodium acetate trihydrate,
(Pa2) a step of melting the heat storage material at 80 degrees Celsius or less after the step (pa1),
(A) cooling a heat storage device including the heat storage material to bring the sodium acetate trihydrate into a supercooled state,
here,
The heat storage device is included in the vehicle,
The heat storage device,
The heat storage material in contact, and silver, a silver alloy or a first electrode having a surface formed from a silver compound,,
A second electrode in contact with the heat storage material,
An inorganic porous material contained in the heat storage material; and a power supply for applying a voltage to the first electrode and the second electrode,
The inorganic porous material has an average pore diameter of 10 nanometers or more and 50 nanometers or less, and the inorganic porous material is formed of silica gel,
(B) A step of applying a voltage to the first electrode and the second electrode using the power source at a temperature of 58 degrees Celsius or less, and applying the heat to the engine by releasing heat from the heat storage material. And (c) after the step (b), a step of heating the heat storage device at a temperature of 58° C. or higher and 80° C. or lower to melt the sodium acetate trihydrate. The method of claim 4, wherein
The step (pa1) is
(Pa11) A method comprising a step of cooling the heat storage material to -30 degrees Celsius or less. The method of claim 4, wherein
The step (pa1) is
(Pa12) A method comprising a step of adding crystals of sodium acetate trihydrate to the supercooled heat storage material.

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